Recently emerging types of electronic devices such as solid-state drives (SSDs) comprise a backup power supply. A capacitor of an electric double layer type is commonly used as such a backup power supply.
Degradation of a capacitor appears as a change in the capacitance of the capacitor. Thus, it is known that the capacitance of the capacitor is detected in order to predict possible rapid degradation of the capacitor. It is also known that the capacitance of the capacitor is detected (or measured) by utilizing transient response characteristics observed when the charge stored in the capacitor is discharged.
The recent electronic devices having a capacitor as a backup power supply provide an intermittent charging control function to intermittently charge the capacitor in order to prevent possible overcharging that may cause the capacitor to be degraded. Immediately after charging or with the capacitor intermittently charged, a voltage applied to the capacitor (that is, the terminal voltage of the capacitor) is not constant. In such a state, the capacitance of the capacitor is not saturated. Thus, accurately detecting the capacitance utilizing the transient response characteristics is difficult.